CURRENT PRE- CAMBRIAN LITER A TURE 1 99 



Of the pre-Animikie rocks, the greenstones and clastic rocks have 

 been called Keewatin. As the greenstones are usually associated with 

 the Mesabi iron-bearing rocks, these alone of the Keewatin rocks are 

 described. They lie to the north of the iron-bearing rocks in T. 65 

 N., R. 5 W., and extend eastward to the center of T. 65 N., R. 4 

 W., where they disappear under the Animikie strata. In general, 

 the greenstones are at present diorites ; originally some were cer- 

 tainly diabases, others were of the nature of andesites, and a large part 

 were diorites, or possibly gabbros. At places, especially along the 

 east side of Sec. 27, T. 65 N., R. 5 W., the greenstones contain angular 

 and subangular fragments of rock almost like themselves, and some 

 may be regarded as composed of fragmental volcanic rocks. Asso- 

 ciated with the greenstones, especially in Sees. 22, 23, and 24, T. 65 N., 

 R. 5 W., are small masses of more acid rocks, quartz porphyries and 

 quartzless porphyries, which are probably younger than the green- 

 stones. 



The pre-Animikie granite has its typical development on the shores 

 of Saganaga Lake. In a number of places it may be seen in intru- 

 sive relations with the greenstone. A quarter of a mile south of the 

 N. E. corner of Sec. 23, T. 65 N., R. 5 W., many granite dikes cutting 

 the greenstone are seen, and on the south shore of West Seagull Lake 

 granite dikes of the same nature as the immediately adjacent main 

 mass of Saganaga granite are seen cutting the greenstone. Both 

 granite and greenstone are cut by another series of finer grained, more 

 acid granite dikes. 



The Animikie rocks rest unconformably upon the pre-Animikie 

 rocks, and usually on the southern slope of the Giant's Range, which 

 is composed essentially of granite. The strike is approximately 

 E. N. E., and the dip in general about io° E. of S. The thickness 

 varies from nothing to 4000 feet. The Animikie is separable into four 

 conformable divisions : ( 1 ) the lower or quartzite member, called the 

 Pewabic quartzite; (2) the iron-bearing or taconyte member; (3) the 

 black slate member ; (4) the graywacke-slate member. 



(1) The quartzite member is well developed in Itasca county, but 

 disappears before reaching the eastern side of St. Louis county. 



(2) The rocks of the iron -bearing member are similar to those in 

 St. Louis county on the western end of the range, described by Spurr. 1 

 They differ, however, in two features. They are more completely 



'Geol. and Nat. Hist. Surv. of Minn., Bull. X, 1894. 



